Ruby on Rails: Insert values via form into array field in db

How would you insert values from a form into an array in the database? I'm using simple form, rails 4.1, postgresql db.

Here is my form, all fields update correctly except for the impact and likelihood fields (both arrays). They are the focus of this question:

<%= simple_form_for(@risk) do |f| %>
  <%= render 'shared/error_messages', object: f.object %>
  <div class="form-group">
    <%= f.input :title, required: false, :error => false, input_html: { class: 'form-control' } %>
  </div>

  <div class="form-group">
    <%= f.input :description, required: false, :error => false,  as: :text, input_html: { class: 'form-control description' } %>
  </div>

  <div class="form-group">
    <%= f.input :area, :collection => ['Operations', 'IT', 'Finance'], required: false, :error => false, input_html: { class: 'form-control' } %>
  </div>

  <div class="form-group">
    <%= f.input :owner, :collection => User.all, required: false, :error => false, input_html: { class: 'form-control' } %>
  </div>

  <div class="form-group">
    <%= f.input :action, required: false, :error => false, input_html: { class: 'form-control' } %>
  </div>

  <div class="form-inline">
    <span class="date-of-action-input">
    <%= f.input :date_of_action, :as => :date, :start_year => Date.today.year - 10, :end_year => 2030,
        :order => [ :day, :month, :year], :required => false, :error => false, input_html: { class: 'form-control' } %>
    </span>
    <span class="action-completed-input">
    <%= f.input :action_completed, as: :boolean, required: false, :error => false, input_html: { class: 'form-control' } %>
    </span>

    <span class="impact-input">
    <%= f.input :impact, required: false, :error => false, input_html: { class: 'form-control' } %>
    </span>
    <span class="likelihood-input">
    <%= f.input :likelihood, required: false, :error => false, input_html: { class: 'form-control' } %>
    </span>
    <span class="submit-risk">
    <%= f.button :submit, :error => false, :error => false, input_html: { class: 'form-control' } %>
    </span>
  </div>
<% end %>

Here the associated controller (risks_controller.rb):

class RisksController < ApplicationController
before_action :signed_in_user
before_action :correct_user, only: [:destroy, :update]


def create
    @risk = current_user.risks.build(risk_params)
    if @risk.save
      flash[:success] = "Risk created!"
      redirect_to root_url
    else
      render 'new'
    end
end

def new
  @risk = Risk.new
end

def destroy
  @risk.destroy
  redirect_to root_url
end

def edit
  @risk = Risk.find(params[:id])
end

def update
  @risk = Risk.find(params[:id])
    @risk.assign_attributes(risk_params)
    if @risk.changed? == false
      flash[:info] = "No changes were made"
      redirect_to root_url
    elsif @risk.update_attributes(risk_params)
      flash[:success] = "The risk has been updated."
      redirect_to root_url
    else
        render 'new'
    end
end

private

    def risk_params
        params.require(:risk).permit(:description, :title, :area, :owner, :action, :date_of_action, :action_completed, :impact, :likelihood)
    end

  def correct_user
    if current_user.admin?
      @risk = Risk.find_by(id: params[:id])
      redirect_to root_url if @risk.nil?
    else
      @risk = current_user.risks.find_by(id: params[:id])
      redirect_to root_url if @risk.nil?
    end
  end

end

My db schema file:

ActiveRecord::Schema.define(version: 20140617165640) do

  create_table "risks", force: true do |t|
    t.integer  "user_id"
    t.string   "description"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "title"
    t.string   "area"
    t.string   "owner"
    t.string   "action"
    t.date     "date_of_action"
    t.boolean  "action_completed", default: false
    t.integer  "impact",           default: [],    array: true
    t.integer  "likelihood",       default: [],    array: true
  end

  add_index "risks", ["user_id", "created_at"], name: "index_risks_on_user_id_and_created_at", using: :btree

  create_table "users", force: true do |t|
    t.string   "name"
    t.string   "email"
    t.boolean  "admin",           default: false
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "password_digest"
    t.string   "remember_token"
  end

  add_index "users", ["email"], name: "index_users_on_email", unique: true, using: :btree
  add_index "users", ["remember_token"], name: "index_users_on_remember_token", using: :btree

end

I imagined the code would look something like this, but alas, my first rails project and I need a bit of guidance. In risks_controller.rb:

def create
  @risk = current_user.risks.build(risk_params)
  @impact = risk_params[:impact]
  @userid = current_user.id
  @impacttoupdate = Risk.select(:impact).where(id: risk_params[:id])
  @impacttoupdate.insert(@userid, @impact)
    if @risk.save
      flash[:success] = "Risk created!"
      redirect_to root_url
    else
      render 'new'
    end
end

I want to insert the value according to the user id. So if the user id is 3, the value from the form they are submitting should go into the 3rd slot in the array.